Continuous laminating method and apparatus



Aug. 6, 1968 R. F. HOFFMANN CONTINUOUS LAMINATING METHOD AND APPARATUS Filed Jan. 10, 1964 INVE NTOR REUBEN F. HOFFMANN BY ATTORNEY.

3,396,064 CONTINUOUS LAMINATING METHOD AND APPARATUS Reuben F. Hofimann, Algoma, Wis., assignor to U.S. Plywood-Champion Papers Inc., a corporation of New York Filed Jan. 10, 1964, Ser. No. 337,012 10 Claims. (Cl. 156-335) ABSTRACT OF THE DISCLOSURE This invention is concerned with a composition and a process for the preparation of bonded materials utilizing especially prepared adhesive mixtures or compositions. The invention is more particularly concerned with an improved technique for the application of the adhesive to the plies whereby the plies can be laid up in a very effective and efiicient manner over processes heretofore employed. Plies of wood and other lignocellulose materials, such as, laminated beams or frames, and plywood, hardboard and particle board panels for structural purposes, doors, partitions, etc., are particularly suitable.

In accordance with a specific adaptation of the present invention, the plies are coated utilizing a precatalyzed phenolic wet line application technique and adhesive; and are handled in a manner to permit substantially greater production of fibrous panels of improved quality. In esence, the adhesive is a resorcinol type, alkali catalyzed, spray dried, phenol-formaldehyde resin (synthetics Expand Adhesive Functions by Peter W. Sherwood, published in Hitchcocks Wood Working Digest, page 23, August 1963, Hitchcock Publications, 222. E. Willow, Wheaton, 111.).

It is known to prepare panels comprising two or more plies 'by first producing the respective plies, and thereafter applying an adhesive which generally comprises using a conventional Wet glue. The glue is caused to set by placing in either a hot press or a cold press for the required time. Alternatively, a dry film may be inserted between the plies, and thereafter placing the unit in a hot press to cause permanent adhesion of the plies.

For instance, a technique heretofore employed is to cut the dried film to size and insert between the plies to form a sandwich at the time of lay-up. This, in effect, comprises a relative slow process as compared to the technique of the present invention which, in essence, comprises the utilization of a precatalyzed phenolic wet line process having the handling advantages of a dry glue line lay up.

The process of the present invention may be readily understood by reference to the diagrammatic flow plan illustrating one embodiment of the same. Referring specifically to the flow plan, a crossband or ply 1 is shown moving along a production line or conveyor 2. This conveyor in essence comprises two or more continuous strands which are adapted to move the respective plies or crossbands through the respective processing steps.

In a first stage of the line, ply 1 passes beneath a conventional roll glue spreader 3. Here a precatalyzed phenolic adhesive or glue is applied to both surfaces of the ply, preferably 28 to 37 lbs./ 1000 sq. ft. of single glue States Patent "ice line. In essence, the formulation of the especially prepared glue or adhesive of the present invention is as follows:

1 Chapter 22, Handbook of Adhesives, edited by Irving Skeist, Reinhold, New York, 1962. There are two basic classes of phenolic resins: resols and novolacs. Both begin as phenol alcohols regardless of whether the catalyst is acid or alkaline. When phenol and excess formaldehyde are reacted in the presence of alkali the reaction products contain metholyl side or end groups which are the resols. They are cured to the final or 0 stage by heat; hence they are commonly called one-stage resins. The cured resin is termed a resite. The so-called water soluble phenolic resins are actually dispersions of resols in alkaline solution. It is these mixtures which are the basis of the exterior plywood adhesives oi the present invention.

2 The pecan or walnut-shell flour is present in order to prevent excessive penetration into the wood during coating and pressing and thus prevent starved glue lines and wasted adhesive.

In the very early stage of the reaction between the phenol and the excess formaldehyde, a resin is water soluble, which is very desirable, but is too slow curing to be practical and economical because the reaction is so far from complete.

As the reaction is advanced, the phenolic resin in the so-called B stage becomes less and less soluble in water. As pointed out, the common procedure is to increase the alkalinity until finally a very strong alkaline solution results which holds the resin in a sort of sol or suspension. The alkali, or catalyst is any suitable alkali solution as, for example, sodium or potassium hydroxide, particularly sodium hydroxide.

In accordance with the present invention, instead of advancing the resin to the point where a strong alkali is necessary in order to maintain solution, an aliphatic alcohol is added. This alcohol may be any suitable low boiling alcohol as, for example, methyl alcohol, ethyl alcohol, isopropyl alcohol or a mixture. In general, the alcohol should have from about 1 to 4 carbon atoms in the molecule. By using a relatively low boiling alcohol, good solubility is achieved in spite of the advancement.

By using adhesive or phenolic resin solutions as described, the wood surface may be readily coated, and a film is formed which acts like a varnish. These films may be readily dried under mild heat without accidentally precuring the resin, partly because of the lesser quantity of alkali present and partly because of the less advanced condition of the resin.

The alcohol present has an additional advantage in that being much more volatile than water, it will be removed more readily and will also be independent of the relative humidity. This greatly aids in the drying since less heat will be required and, accordingly, less danger will exist on precuring of the resin.

Thus, the catalyst or alkali used in the preparation of the adhesive is preferably sodium hydroxide or its equivalent in alkalinity. The methanol or other aliphatic alcohol is an essential ingredient. Furthermore, these resins must dissolve in a water-alcohol mixture if the results desired by the present invention are to be secured. Resins that will function of the resol type are soluble in water-alcohol mixtures, all alcohol, alcohol acetone mixtures or all acetone, and the like.

The adhesive is preferably applied at room or ambient temperatures as, for example, in the range from about 68 to 85 R, such as about F The ply, after having the adhesive applied by spreader or rolls 3, then passes into evaporation zone or area 4 wherein substantially all the solvent is removed. By evaporation area is meant an unenclosed area or a partially enclosed chamber vented for removal of solvent vapors. The Perlon* strands carrying the respective plies along the production line are cooled in evaporation area 4 by means of cooling water or cooling fluid circulated through pipes or conduits 15. This serves to prevent the resin or adhesive from sticking to the conveying strands.

The solvent is removed by circulating air at a temperature in the range from about 45 F. to 55 F. as, for example, about 50 F. across the top and bottom of the ply. As pointed out heretofore, flashing or removal of the solvent is readily and effectively secured by using a low boiling alcohol.

The ply, after passing through flash Zone 4, then passes into an infrared oven zone wherein both the top and the bottom of the ply are heated by infrared ovens 5 and 6. Here the precatalyzed adhesive is advanced. The preferred temperatures for use with respect to ovens 5 and 6 is in the range from about 145 to 175 R, such as 160 to 170 F., and the time period in the range from about to 60 seconds especially in the range from to 50 seconds. A preferred method of precuring is at a temperature of about 160 F. for a time period of about seconds.

The infrared ovens are important. Resols are particularly susceptible to heating by infrared and the drying begins at the bottom of the film, thus getting the solvents out as quickly as possible and with the least danger of precuring. Convection ovens and high-velocity ovens would merely skin over such a varnish coat causing sticking later and perhaps starved glue lines in the pressing operation. While infrared ovens are much preferred, it is understood that advancing may be accomplished by circulating air in heated ovens as, for example, at a temperature in the range from about 145 to 300 F. for a time period in the range from about 30 to 40 seconds.

After the ply or crossband passes through the infrared ovens 5 and 6, it is passed through cooling units 7 and 8 wherein the ply is rapidly cooled to ambient temperature. The cooling unit is necessary in order to prevent latent heat from advancing the cure too far; it is desirable to stop the advancement quickly. This is accomplished by circulating cool air cooled by means of cooling water or cooling fluid circulated through pipes or conduits 15, over the top and bottom of the ply or crossband at a temperature in the range from about 0 F. to F., preferably at a temperature in the range from about 20-40 F. The cooled plies are then passed to a lay up step 9 wherein the same are manually afiixed one to the other, which is accomplished very effectively and in a relatively short time as compared to the dry film method.

The laid up unit is then stacked and then fed into the hot press 10 and 11 where they are finally cured, preferably at a temperature in the range from about 280 to 320 F. for a time period in the range from about 3 to 10 minutes. The pressures utilized are in the range from about to 200 pounds per square inch. A very desirable temperature is in the range from 290 to 310 R, such as about 300 F. for a time period of from 5 to 8 minutes, such as about 6 minutes. A very desirable pressure is in the range from about to 175 lbs/sq. in., such as about lbs/sq. in.

By operating as described heretofore, a number of distinct advantages and high quality products are secured. For example, there exists a minimum glue bleed-through when using decorative face veneers, i.e., penetrating and visible in spots on the outside surface. Furthermore, the technique and glue compositions of the present invention eliminates laps and splits. Also, in processes heretofore employed, wet and dry film lines have lead to blows. The present process substantially eliminates this difficulty. Furthermore, the throughput is effectively and materially increased and the quality improved.

In accordance with the present invention, it is very A registered trademark for synthetic fiber obtained by polymerization of ecaprolactum Pcrlon is known as nylon 6 polymer in the U.-S.A. Merck Index, 7 ed., p. 787.

essential that the precuring or advancing operation be within the range specified otherwise the cure will be too advanced, with the result that in the final hot pressing operation, an inadequate bond or a defective bond will be secured between the respective plies. Furthermore, by using the present technique, the moisture content of the materials is not as critical as when employing other techniques such as a dry film process. As pointed out heretofore, in the dry film process the film must be cut to size and inserted between the respective plies at the time of lay up. The present process eliminates this slow technique and the lay up crews are tied in with direct machine line speed.

The present invention may be understood by the following example illustrating an embodiment of the same.

Example A phenolic adhesive of the following formulation was prepared: The formula may be somewhat varied depending upon desired viscosity.

Materials: Percentage Phenolic resin 1 45.0 Water 33.7 Walnut shell 11.2 Methanol 10.1

Phenol was reacted with an excess of formaldehyde and a minimum of al ali until a B stage resin was secured. This resin was still soluble in water but not freely so, but quite soluble in water-alcohol mixtures. In general, these resins which are soluble in low boiling alcohols, or acetone and in water-alcohol mixtures are satisfactory. Adhesives that will not function in the present invention are those which are soluble exclusively in strong caustic aqueous mixtures,

The adhesive after mixing was fed into a conventional top and bottom glue spreader. The spreader applied a uniform application of resin to each side of the component passing through the spreader rollers. The rate of spread was 28 to 37 pounds of adhesive per thousand square feet of single glue line. The spread component emerges from the spreader onto a Perlon or plastic type strand conveyor. The conveyor consists of continuous strands, and conventional water cooled attachments cooled by means of cooling water circulating through pipes or conduits 15" (similar to 15 and 15') are positioned where desirable along the operating or the return path to keep the strands cool and thus prevents the adhesive sticking to the strands.

The spread material was immediately flashed off as described by means of circulating air and then semiadvanced in an infrared oven. The infrared oven was 21 feet long and operating at approximately F. for 45 seconds. The infrared heating elements are located at the top and bottom of the ovens. As the material emerged from the infrared oven it was immediately cooled in the cooling units. The crossbands were then sent to the lay up station and the hot press area as described. Excellent high quality panels of high strengths were secured.

The above procedure may be utilized for fabricating various types of substrates and construction elements per taining to cross-laminating. Thus, the spread material may be laid up into a regular door, partition or other plywood constructions and cured as, for example, via the hot press methods at temperature ranges from about 280 F. to 320 F. for about 3 to 10 minutes depending on the depth to the farthest glue line, and at pressures in the range from about 110 to 200 pounds per square inch depending on the particular construction.

What is claimed it:

1. Process for the fabrication of a panel in a fast, substantially continuous process to increase through-put, and increase quality by eliminating starved glue lines consist-- ing of a plurality of plies which comprises the steps of coating said plies with an alkali catalyzed phenol formal dehyde resin present in a solution containing a monohydroxy aliphatic alcohol, removing said alcohol by atmospheric air, thereafter moving said plies by thin con- See footnote at hot-tom of column 3.

veyor strands, cooling said strands and subjecting said plies coated with said resin to heat, followed by rapid cooling of the heated coated plies to prevent advancing the cure of the resin too far, thereafter laying up the respective plies and finally applying heat to bond the assembly together.

2. Process as defined by claim 1 wherein circulating air is passed over said alcohol to evaporate said alcohol, and said air being at a temperature in the range from about to F.

3. Process as defined by claim 2 for use with plies having a wide range of moisture content, and to minimize glue bleed-through, laps and splits, wherein infrared heat is applied to said coated plies to eliminate the solvents and wherein the temperature is in the range from about 145 to 175 F., and subjecting said plies to said temperatures for a period from about 35 to seconds.

4. Process as defined by claim 3 wherein said plies are coated wood plies and are moved from said infrared heat, subsequently are rapidly cooled to prevent an advanced cure of said resin, and subjecting the assembly to a final bonding temperature in the range from about 280 to 320 F., for a period from about 13 to 10 minutes, under pressure in the range from to 200 lbs/sq. in.

5. Process as defined by claim 4 wherein said wood plies are coated on both sides, moving the coated Wood plies by plastic strands from one operation to another, and cooling the plastic strands while passing low temperature air over said coating to evaporate the solvents.

6. Process for bonding a wood panel as defined by claim 1 wherein the temperature for evaporating solvents is in the range from about 50 F., wherein the infrared heating temperature is in the range from about to F. for a period from about 40 to 50 seconds, and

the final bonding is in the range from about 290 to 310 F.

for a period of from 5 to 8 minutes, at pressures in the range from 125 to lbs/sq. in.

7. Process as set forth in claim 6 wherein the phenol formaldehyde resin is formed by adding the following weight percentages: phenolic resin 64-21, water 25-45, shell flour 6-14, and methanol 520.

8. Process as set forth in claim 1 wherein the phenol formaldehyde resin is formed by adding the following Weight percentages: phenolic resin 45, water 33.7, walnut shell flour 11.2, and methanol 10.1

9. An apparatus to apply precatalyzed adhesive to a ply in a fast, substantially continuous process to increase through-put, and increase quality by eliminating starved glue lines, comprising a conveyor comprising at least two strands of plastic, an adhesive spreader to apply an adhesive to both sides of said ply, an evaporation area to evaporate the low boiling solvent, means to cool the said conveying strands to prevent sticking to the adhesive, infrared ovens to advance the setting of the adhesive, a lay-up area, and a hot pressing means for bonding the assembly together.

10. An apparatus as set forth in claim 9 for multiple plies of Wood veneer, and cooling units are used after the infrared ovens to prevent the cure from advancing so far that it reaches its final setting stage.

References Cited UNITED STATES PATENTS 2,885,068 5/1959 Bishop 198229 2,482,525 9/1949 Wachter 26029.3 2,574,784 11/ 1951 Heritage 156-335 2,699,417 1/1955 Repsher et al 161259 3,008,907 11/1961 Williams 117-148 FOREIGN PATENTS 684,860 12/1952 Great Britain.

OTHER REFERENCES Sneeden, J. 0.: Applied Heat for Engineers, Blackie and Son, Ltd., London (1960), page 115.

Turner et al.: Condensed Chemical Dictionary, Rheinhold, New York, 1950, page 7.

EARL M. BERGERT, Primary Examiner.

W. E. HOAG, Assistant Examiner. 

